A solder of a contact mainly provides electric conductivity and mechanical strength disposed between an electronic component and a circuit board and is a path for spreading heat during operation, and therefore the solder is very important to an electronic product. Conventional tin-lead (Sn-Pb) solder has low cost, good wetting property, proper fusing point, proper electric conductivity, proper mechanical strength and proper thermal conductivity, and therefore tin-lead (Sn-Pb) solder has been widely applied in the field of industry. However, lead (Pb) is a toxic heavy metal, and seriously affects the health of a human body. Thus, various countries gradually instituted laws and decrees to restrain or stop using the solder with lead. In 1998, a conference of global same trade organization was held in Wiesbaden, Germany by PCB makers from various countries, and it was concluded that various countries would stop using the solder with lead commencing in 2004. Although the conclusion to stop using the solder with lead was changed from 2004 to July, 2006 for some reason, the lead-free solder would still become a challenge for the electronic industry in the future.
When the Nano-scale Electronic Age began, electronic devices leaned towards minimization, low lightweight and high functional requirement and electronic packaging technology leaned towards higher I/O density and shorter contact pitch. Thus, the high density connection technologies, such as flip chip connection, chip scale package (CSP) and direct chip attachment (DCA), became the main stream of the future electronic packaging technology, but the technology of connection between components became a key technology.
As the minimization of an integrated circuit (IC) and the complexity of a circuit are required, the soldering point of the corresponding electronic component leans towards minimization. Conventional solder is formed by “an electroplate method” or “a silk screen printing method”. However, the above-mentioned methods mostly form micrometer-scale solder (100˜1000 nm), and cannot form a useful Nano-scale (0.1˜100 nm) lead-free solder according to the Nano-scale (0.1˜100 nm) soldering point of the electronic component.